1. Field of the Invention
The present invention relates to methods and apparatus for feeding back channel quality indication in a communication system.
2. Description of the Related Art
This application, pursuant to 37 C.F.R. §1.57, incorporates by reference the following publications:
[1] 3GPP R1-075037, “Draft Change Request to TS 36.212 v8.0.0”;
[2] 3GPP R1-075069, “Summary of AH session on AI 6.4.5 “UE Procedures for downlink shared channel””, Samsung;
[3] “[LTE] CQI table construction”, email discussions on 3GPP RAN1 email reflector.
Table 1 shows an example of a channel quality indication (CQI) table. Each CQI index of the table represents the channel condition estimated by a mobile station (i.e., User Equipment or UE). For a given channel condition, the most appropriate CQI index is selected and fed back by the mobile station. As an example, as shown in Table 1, if CQI index 9 is reported, the UE recommends modulation and coding scheme (MCS) as quadrature phase-shift keying (QPSK), 1/4 code rate (64/256=1/4). Note that this recommendation only serves as an input for the base station (i.e., Node B) to make a scheduling decision. The Node B may or may not follow the recommendation by the UE. Also note that there are various ways of constructing the table. For example, the table may be constructed with a subset of the columns as shown in Table 1. As an example, the table may consist of the CQI index column, the modulation column, and the code rate column. Or, alternatively, the table may consist of the CQI index column, the nominal transport block size (TBS) column, and (optionally) the modulation column.
TABLE 1An example of CQI tableCQICode Rate ×Nominal spectral NominalindexModulation256efficiencyTBS0N/AN/AN/AN/A1QPSK100.078125402QPSK130.1015625483QPSK160.125644QPSK200.15625725QPSK260.203125966QPSK320.251207QPSK400.31251528QPSK510.39843751929QPSK640.524010QPSK830.648437531211QPSK1000.7812537612QPSK1200.937544813QPSK1401.0937552814QPSK1611.25781256081516 QAM841.31256241616 QAM1001.56257521716 QAM1151.7968758641816 QAM1312.0468759761916 QAM1472.29687510882016 QAM1632.54687512162116 QAM1812.82812513442216 QAM1993.10937515042364 QAM1383.23437515682464 QAM1513.539062516962564 QAM1653.867187518562664 QAM1794.195312520162764 QAM1944.54687521762864 QAM2094.898437523682964 QAM2215.179687524963064 QAM2315.414062526243164 QAM2365.531252688
Contemporarily, when a UE feeds back a CQI index selected from Table 1, the UE has to use 5 bits for the CQI index, which creates a large overhead for the control signal.